Now what's interesting about the mitochondria and the mitochondrial DNA is they are not passed along with the chromosomes as are most genes in our cells, but they are passed through the egg of the mother at fertilization. And that's because the egg has about 200,000 mitochondria whereas the sperm have just a few, and those that do enter the egg are actually destroyed. So in fact then, the mitochondria and their DNA are inherited exclusively from the mother.